One of the best ways to learn about a planet's history is to examine its geology, so one of the things scientists look for when sending rovers to Mars is areas on the planet's surface that allow access to multiple layers of diverse and interesting rock types.

Ancient bedrock can be tilted, folded, and generally complicated and difficult to understand, but the center of this image [13.2 Mb hi-res version available here] shows a stack of nearly horizontal layers. These layers might record how the environment on ancient Mars changed over time, and would be a good site for future exploration by a rover.